The present invention relates to an apparatus which detects the rotational angle and/or the number of rotations of a rotary body, for example, the crankshaft of an automobile or other engines.
In the automobile industry, the problem of exhaust gas pollution is lately very serious, and for the solution of that problem, the fine control of an engine is desired. For the fine control, detection of the rotational angle and the number of rotations of a crankshaft and/or an engine-shaft is absolutely necessary.
Optical and electromagnetic systems have been proposed for detecting the rotational angle and the number of rotations of automotive rotary bodies. Recently proposed for this purpose are applications of the magnetic sensors using such semi-conductor elements as a Hall element, a magnetoresistance element, etc. The optical system is questionable as to its reliability in a vibration and dust environment, the electromagnetic system has the output voltage varied according to the speed of revolution of an engine, and the systems using semi-conductors are inferior in temperature characteristic, weak against impacts and expensive. Thus, a prior detector of the rotational angle and the number of rotations of the above-mentioned systems present difficulties in automotive use.